These studies will explore the correlation between hypothalamic biogenic amine concentrations and metabolism with changes in LH and Prolactin release occurring in response to electrical stimulation of the dorsal raphe nucleus of the ovariectomized rat in the presence and absence of estrogen. This will be accomplished by pumping through intracerebral dialysis probes an artificial cerebrospinal fluid into which substances present at higher concentrations in the extracellular space of the brain will diffuse across the dialysis membrane down their concentration gradients. Fractions (40 mu1/10 minutes) of dialysate will be collected for analysis by high performance liquid chromatography with electrochemical detection. Studies will be carried out in unanesthetized animals chronically prepared with polyvinyl cannulae in the right external jugular vein for collection of blood samples for radioimmunoassay of LH and prolactin, and intracranial guide cannulae above the medial preoptic area and medial hypothalamus through which dialysis probes can be inserted and removed at the beginning and end of each experiment. The primary focus will be a comparison of the anatomical location, neurotransmitter identity, and particular receptor species correlated with the opposite changes in LH release induced by stimulation of the dorsal raphe nucleus in the presence and absence of estrogen. Attention will be directed toward the medial preoptic area and the medial and basal region of the hypothalamus, areas commonly associated with stimulatory and inhibitory influences, respectively, on the release of LH. The ability to obtain serial measurements by means of the dialysis technique represents a major advance over the single-time-point analysis of homogenized brain tissue obtained by microdissection. This will allow the temporal sequence(s) of events to be followed, with the hope of testing new hypotheses concerning the role of these neurotransmitter systems in controlling pituitary hormone release, as well as the modulating influences of estrogen on these mechanisms. For instance, the dialysis probe will subsequently be used to deliver to those sites showing changes in 5HT and/or catecholamine function, agonists or antagonists which select among particular receptors in attempts to mimic or prevent events accompanying raphe stimulation. Similarly, the location and nature of the synergism between opiate and 5HT systems in releasing LH in ovariectomized estrogen-progesterone primed rats will be studied by perfusing preoptic or hypothalamic dialysis probes with opiate and/or 5HT agonists or antagonists while following changes in catecholamines and 5HT in the perfusate.